Enzymes of steroid biosynthesis such as the steroid aromatizing system and the 3 beta-01 dehydrogenase-isomerase will be isolated and purified from ovaries and will be characterized with respect to their kinetic and control properties. The action of these and other steroid metabolizing enzymes will be studied by tracer techniques in pregnant women. The molecular mechanism of action of the female sex hormones will be examined by biochemical techniques such as measurement of their receptors and metabolic effects on target tissues in organ and cell culture.